KR20210030348A - Method for manufacturing reflective optical elements of projection exposure apparatus and reflective optical elements for projection exposure apparatus, projection lenses and projection exposure apparatus - Google Patents

Abstract

The present invention is for manufacturing a reflective optical element for a projection exposure apparatus 1 comprising a substrate 30 having a substrate surface 31, a protective layer 38 and a layer sub-system 39 suitable for the EUV wavelength range. A method comprising the steps of: a) measuring the substrate surface 31, b) irradiating the substrate 30 with the aid of an electron 36, c) tempering the substrate 30. will be. Furthermore, the present invention relates to a reflective optical element for the EUV wavelength range. Furthermore, the present invention relates to a projection lens having mirrors 18, 19, 20 as reflective optical elements and a projection exposure apparatus 1 having a projection lens.

Description

Method for manufacturing reflective optical elements of projection exposure apparatus and reflective optical elements for projection exposure apparatus, projection lenses and projection exposure apparatus

This application claims the priority of German patent application DE 10 2018 211 596.6, the content of which is incorporated herein by reference in its entirety.

The present invention relates to a method for manufacturing a reflective optical element of a projection exposure apparatus and a reflective optical element for a projection exposure apparatus. Furthermore, the present invention relates to a microlithographic projection lens comprising such an element and a microlithographic projection exposure apparatus comprising such a projection lens.

Microlithographic projection exposure apparatus for the EUV wavelength range of 5 to 20 nm relies on the fact that the reflective optical element used for imaging of the mask into the image plane has a high accuracy with respect to its surface morphology. Likewise, the mask as a reflective optical element for the EUV wavelength range must have high accuracy with respect to the surface shape, since its use is importantly reflected in the operating cost of the projection exposure apparatus.

Methods for correcting the surface morphology of optical elements, in particular US 6844272 B2, US 6 849 859 B2, DE 102 39 859 A1, US 6 821 682 B1, US 2004 0061868 A1, US 2003 0006214 A1 , US 2003 00081722 A1, US 6 898 011 B2, US 7 083 290 B2, US 7 189 655 B2, US 2003 0058986 A1, DE 10 2007 051 291 A1, EP 1 521 155 A2 and US It is known from 4 298 247.

Some of the correction methods listed in the above mentioned documents are based on locally compressing the substrate material of the optical element by irradiation. As a result, a change in the surface shape of the optical element is achieved in the vicinity of the irradiated area. Another method is based on direct surface ablation of the optical element. Others of the above-described methods then utilize the thermal or electrical deformability of the material to impress spatially extended surface morphology changes on the optical element.

DE 10 2011084117 A1 and WO 2011/020655 A1 disclose methods for protecting reflective optical elements from long-term compression on the order of several volume percent or from aging of substrate materials due to EUV radiation, in addition to correcting the surface morphology. I'm doing it. To this end, the surface of the reflective optical element is homogeneously compressed by radiation and/or coated with a protective layer. Both methods prevent penetration of EUV radiation into the substrate material. As a result, surface deformation as a result of material compression by EUV radiation, which is unacceptable for long-time operation, can be prevented.

The cause of compression or aging of substrate materials such as Schott AG's Zerodur® or Corning Inc.'s ULE® with a composition _{of SiO 2} >40 vol. in), and the unequilibrium state is assumed to be incorporated into a thermodynamic ground state in case of EUV irradiation. In keeping with this hypothesis, it is possible to produce a coating of _{SiO 2} that does not exhibit this compression since these layers are produced at substantially lower temperatures than the substrate material for the appropriately selected coating method.

Disadvantages of all the aforementioned methods for targeted local and homogeneous compression of materials for correcting the surface morphology of the substrate and protecting against long-term changes due to compression are: It does not take into account the change in the shape of the surface caused by it. This compression withdrawal, also hereinafter also referred to as decompaction, is assumed to be based on mitigation of the defect state created in the material by irradiation.

It is an object of the present invention to provide a reflective optical element and a method that overcomes the aforementioned drawbacks of the prior art. Another object of the present invention is to specify a projection lens and a projection exposure apparatus comprising an improved optical element.

This object is achieved by a device having the features of independent claim 1. The dependent claims relate to advantageous modifications and variations of the invention.

The method according to the invention for manufacturing a reflective optical element for a projection exposure apparatus comprising a substrate having a substrate surface, a protective layer and a layer sub-system suitable for the EUV wavelength range:

a) measuring the substrate surface,

b) irradiating the substrate with the help of electrons,

c) tempering the substrate.

As an example, the reflective optical element can be a mirror or a mask. The coating of the substrate may comprise at least one layered partial system optimized for reflection of EUV radiation, ie radiation at a wavelength of 13 nm or 7 nm. This reflective layer may comprise a periodic sequence of at least one period of individual layers, wherein the period may comprise two separate layers with different refractive indices in the EUV wavelength range. However, an aperiodic layer or coating comprising only one layer is also possible.

Optionally, a protective layer may be applied between the substrate and the reflective layer. This protective layer prevents the material underneath from being further compressed by the EUV radiation used, ie the radiation used in the apparatus for exposure purposes. Here, the layer arrangement of the protective layer may comprise a thickness of at least more than 20 nm, in particular more than 50 nm, such that the transmittance of EUV radiation through the layer arrangement is less than 10%, in particular less than 2%. The layered partial system may comprise at least one layer formed or synthesized from a compound from a material of the group of nickel, carbon, boron carbide, cobalt, beryllium, silicon, silicon oxide. These materials firstly have a sufficiently high absorption coefficient for EUV radiation and secondly do not change under EUV radiation. The layer arrangement of the at least one protective layer partial system may also consist of, for example, a periodic sequence of at least two periods of individual layers, the period may comprise two separate layers formed of different materials, and the period The materials of the two separate layers forming a may be nickel and silicon or cobalt and beryllium. Such a layer stack can inhibit the crystal growth of the absorbing metal and consequently provide an overall lower roughness of the layer for an actual reflective coating than would be possible in the case of a pure metal protective layer having a corresponding thickness.

The exact surface morphology of the substrate is ascertained by measuring the substrate surface, which surface morphology generally has a deviation from the intended value. The difference between the measured surface shape of the substrate and the intended surface shape yields the deviation of the substrate surface to be corrected. As a result of local irradiation of the substrate, the substrate is compressed and contracted in the region of 1 μm to 100 μm, preferably 1 μm to 30 μm below the surface, causing deformation on the surface that can correct the substrate surface. Compression depends in particular on the energy and dose of the electrons used for irradiation purposes or the dose received by the material. As an example, the values of energy and dose of electrons may be in the range of ^{5 keV to 80 keV and 0.1 J/mm 2} to 4000 J/mm ^{2, respectively.}

Radiation can also be used to create protection of the substrate against compression going on during its service life as a result of EUV radiation. As a result, the substrate surface can be maximally irradiated with a dose that may be in the region of ^{up to 4000 J/mm 2.} This leads to a saturation of compression, ie a condition in which the compression of the substrate no longer increases, or only increases to a negligible degree in case of further irradiation of the substrate. This compressed region forms a protective layer that protects the rest of the substrate from compression by EUV radiation.

The areas of the substrate material for correcting the surface morphology deviation and for protective compression near the substrate surface can be separated from each other by different penetration depths of the electron beam. Here, the energy for surface correction may be greater than the energy for generating the protective layer. In general, a dose of up to 2500 J/mm ² is sufficient to undertake sufficient surface morphology correction when performing electron irradiation to correct the surface.

The final tempering step results in a partial withdrawal, ie decompression, of the compression of the substrate material previously introduced in the method step. When using a substrate in a projection exposure apparatus such as an EUV projection exposure apparatus, for example, decompression is induced that occurs over time and may thus cause a non-negligible change in the substrate surface. Tempering speeds up the decompression process, so that the remaining changes due to decompression over the service life of the substrate can advantageously be reduced to negligible values.

In an advantageous variant of the invention, the temperature used when tempering the substrate may be in the range of 22° C. to 400° C. Values may range from 22° C. up to 60° C. for tempering in an oven. If the compressed layer is tempered by a laser, the value may preferably be between 150° C. and up to 400° C. In this case, it is established that as the temperature increases, the material can be decompressed more quickly, and as a result, the process time can be advantageously minimized.

The choice of temperature depends on the degree of compression and the geometry of the substrate. The upper limit of the temperature used for tempering purposes is predetermined by the temperature at which the material used for the substrate changes irreversibly or loses its shape. By way of example, the material used for the substrate may be SiSic, Zerodur® from Schott AG or ULE® from Corning Inc. or quartz glass or any other type of glass.

In another advantageous variant of the invention, the temperature can be maintained over a period of 1 hour to 1000 hours when tempering the substrate.

The decompression obtained during tempering depends on the temperature employed, the degree of compression before tempering, the geometry of the substrate and the period during which the temperature is maintained. What is generally applied is that the duration of the tempering process is shorter in the case of small changes in the surface of the substrate, ie in the degree of compression of the substrate before tempering, and vice versa.

In another advantageous variant of the invention, the temperature can change over time when tempering the substrate.

The temperature may vary over time, for example to achieve maximum decompression and/or a reduction in holding time with the same decompression.

In another advantageous variant of the invention, the substrate can be heated in a homogeneous manner during tempering.

Homogeneous heating of the entire substrate for tempering is advantageous in that the substrate is tempered very uniformly and as a result no additional stress is introduced into the material during tempering as a result of the temperature gradient. As an example, the temperature required for tempering purposes can be introduced into the substrate by irradiation with a laser. The substrate can be heated in a homogeneous manner through suitable adjustment of the energy and penetration depth of the laser and/or by attaching a heat sink to affect the heat flow in the material. Alternatively, the substrate may also be heated to a certain temperature, for example in an oven, and cooled again after a certain holding time, as is known from the tempering of a work piece made of metal. This process is advantageous in that known and available equipment can be used. Moreover, the process is simple, which has a positive effect on the manufacturing cost.

In another advantageous variant of the invention, the substrate can be locally heated during tempering.

Depending on the compression undertaken to correct the geometry of the substrate and the surface shape of the substrate, it may be advantageous to achieve the temperature required to temper the substrate through local heating of the substrate without homogeneously heating the substrate. Local heating can be achieved by radiation on the substrate surface, for example by means of a laser or lamp. The wavelength of radiation should preferably be in a region where the reflective coating has a high transmittance and the substrate has a high absorption. The advantage of local heating is that higher temperatures can be set in the compressed area of the substrate. As an example, during the final production of the substrate surface, the reflective optical element may be pre-assembled in a holder which may be exposed only to relatively low temperatures, for example up to 60° C. or less. As a result of local heating and complementary measures to dissipate heat locally, the temperature of the substrate may reach a maximum of 400°C locally, for example the temperature sensitive region of the reflective optical element does not reach its critical temperature. . As a result, the holding time can be advantageously reduced and thus the manufacturing cost can be minimized.

In another advantageous variant of the invention, the temperature can be introduced into the substrate by irradiation with a laser having a wavelength of 2.6 μm to 2.8 μm, in particular 2.755 μm.

The substrate material employed has a component of 40% by volume of SiO _{2 , where the OH groups introduced into the SiO 2} network have resonance at a wavelength of 2.755 μm. Absorption at this wavelength is particularly high as a result of the excitation of the resonance, as a result of which an increase in the temperature of the substrate can be realized more quickly and/or a higher temperature of the substrate can be reached than at other wavelengths.

In another advantageous variant of the invention, the change of the substrate as a result of tempering can be taken into account during the irradiation of the substrate in method step b).

Tests have shown that the change of the substrate during decompression is nearly homogeneous across the material and only a small negligible component of the change is heterogeneous. The advantage of this effect is that, as a result, very accurate prediction of decompression is possible with the aid of testing of the substrate, suitable computational models and FEM models. The compression of the material can likewise be predicted well, and thus advantageously, decompression by tempering can be considered in advance during compression of the substrate, for example by permitting. Accordingly, it is possible to predict the geometric shape of the substrate surface after tempering and to implement it with the required accuracy.

The method also described above can also be applied to the correction of previously manufactured reflective optical elements. After measuring the substrate surface including the pre-coated coating, the substrate can be irradiated with ^{an energy of 5 to 80 keV and a dose of 0.1 J/mm 2} to 2500 J/mm ^{2 to correct for local deformation of the substrate surface.} . Tempering after irradiation can be performed in the same manner as the method also described above. Prediction of compression and decompression of the substrate by radiation and tempering is also possible, as in the case of the manufacture of reflective optical elements, as well. As a result, the reduction in correction of the substrate surface by decompression during irradiation, ie the compression of the substrate, can be kept available to achieve a favorable minimum deviation of the substrate surface from the intended value of the surface.

The present invention further comprises a reflective optical element for the EUV wavelength range comprising a layer arrangement applied to the surface of the substrate, the layer arrangement comprising at least one layer portion system. The substrate has an average density greater than 0.1% by volume higher than the average density of the substrate at a distance of 1 mm from the surface, in the area of the surface adjacent to the layer arrangement up to a distance of 5 μm from the surface. Moreover, the substrate has a density change of more than 0.1% by volume along at least an imaginary area at a fixed distance of at least 1 μm to 100 μm, preferably 1 μm to 30 μm from the surface. Here, at a distance of 1 mm from the surface, the temporal change in density more than 0.1% by volume higher than the average density of the substrate is less than 20% in the first 7 years after manufacture of the optical element.

The dimensional stability of the substrate directly affects the substrate surface and thus the imaging quality of the optical elements. Deformation of the substrate surface as a result of heating of the reflective optical element during operation can be compensated for by cooling or a suitable manipulator. For example, changes in the surface of the substrate as a result of long-term effects that may be caused by changes in the substrate over time as a result of decompression are likewise compensable by the manipulator. However, the order of changes in the substrate surface may be in a range that may exceed the limited movement of the manipulator, especially in combination with deformation caused by heating during operation. As a result of the substrate having long-term stability, this component can advantageously be minimized to an acceptable value.

Furthermore, the present invention includes a microlithographic projection lens comprising a mirror as a reflective optical element according to an embodiment also described above and/or a mirror as a reflective optical element manufactured according to one of the methods also described above.

The microlithographic projection lens is exposed to high loads by the used radiation whose wavelength is preferably 13.5 nm, and radiation at other wavelengths, as a result of which the microlithographic projection lens is heated during operation. By using one of the mirrors also described above, the change of the mirror surface over time as a result of decompression of the material can be advantageously minimized.

Moreover, the present invention includes a microlithographic projection exposure apparatus comprising a projection lens according to the embodiment also described above.

The projection exposure apparatus is operated continuously for 24 hours, and all defects affect the performance of the projection exposure apparatus. The service time of the projection exposure apparatus can advantageously be reduced by the use of a projection optical unit with long-term stability.

Exemplary embodiments and variations of the invention are described in more detail below with reference to the drawings, wherein:
1 shows a basic configuration of an EUV projection exposure apparatus that can be implemented in the present invention.
2a) to 2c) show schematic diagrams of a method according to the invention for manufacturing an optical element according to the invention.
3 a) to 3 c) show schematic views of the surface form of an element according to the invention through a process.

1 shows as an example the basic configuration of a microlithographic EUV projection exposure apparatus 1 in which the present invention can be used. The illumination system of the projection exposure apparatus 1 comprises, in addition to the light source 3, an illumination optical unit 4 for illumination of the objective field 5 in the objective plane 6. EUV radiation 14 in the form of optically used radiation generated by the light source 3 passes through the intermediate focal point in the area of the intermediate focal plane 15 before it is incident on the field facet mirror 2 In this way, it is aligned by a condenser integrated in the light source 3. Downstream of the field facet mirror 2, EUV radiation 14 is reflected by the pupil facet face mirror 16. With the aid of the pupil facet mirror 16 and the optical assembly 17 with the mirrors 18, 19, 20, the field facet face of the field facet face mirror 2 is imaged into the objective field 5.

A reticle 7 arranged in the objective field 5 and held by a schematically illustrated reticle holder 8 is illuminated. The projection optical unit 9, which is shown only schematically, serves to image the objective field 5 in the image field 10 in the image plane 11. The structure on the reticle 7 is imaged on the photosensitive layer of the wafer 12 arranged in the area of the image field 10 in the image plane 11 and held by the wafer holder 13, which is likewise partially shown. do. The light source 3 is capable of emitting used radiation in particular in the wavelength range of 5 nm to 30 nm.

The present invention may likewise be applied to a DUV device not shown. The DUV device is in principle set up as the EUV device 1 described above, where the mirror and lens elements can be used as optical elements in the DUV device, and the light source of the DUV device is used in the wavelength range of 100 nm to 300 nm. Emits radiation.

2 shows method steps a) to c) for manufacturing a reflective optical element according to the invention, for example a mirror 18, 19, 20 according to the invention or a reticle 7 according to the invention of FIG. Schematically shows. In method step a), a mirror 18, 19, 20 or reticle 7 is provided, which has a substrate 30 and a protective layer 38 with a layered partial system 39 suitable for reflection in the EUV wavelength range. Includes. The layer sub-system 39 may consist of a periodic sequence of at least one period of individual layers, wherein the period comprises two separate layers with different refractive indices in the EUV wavelength range. The layer sub-system 39 may also consist of only one layer or may comprise a layer system having an aperiodic sequence of layers. The protective layer 38 arranged under the reflective layer 39 should prevent penetration of EUV radiation into the substrate 30. The surface shape 31 of the mirrors 18, 19, 20 or reticle 7 is measured by an interferometer. Measurements by interferometer are not shown in FIG. 2 for clarity. By doing so, it is determined in method step a) that the mirrors 18, 19, 20 or reticle 7 have an undesired surface shape deviation 32 from the desired intended surface shape.

This surface shape deviation 32 is corrected in method step b) by irradiation 33 through compression of the substrate area 34 caused thereby. Radiation 33 is provided by electrons 36 of electron beam source 35. In particular, electron irradiation 33 by electrons 36 having an energy of 5 to 80 keV at a dose of 0.1 J/mm ² to 2500 J/mm ^{2 and/or a wavelength of 0.3 to 3 μm, 1 Hz to 100 MHz} Photon irradiation with the aid of a pulsed laser with a repetition rate of and a pulse energy of 0.01 μJ to 10 mJ can be considered here in particular. As a result of compression of the substrate region 34, a change in the density of the substrate material of more than 0.1% by volume occurs along the virtual region 37 at a fixed distance from the surface, which virtual region forms the compressed substrate region 34. Extends through. Here, the change in density is understood to mean a difference between the maximum value of the density and the minimum value of the density along the virtual area 37 of a certain distance. In the case of a homogeneous irradiation 33 of the substrate area 34, this regimen means that the substrate area 34 has a higher density than that of an adjacent unirradiated area at the same distance from the surface by more than 0.1% by volume. . The correction of the surface shape allows the effect in further procedures and consequently is overcorrected to obtain the desired surface shape after the last method step c). Further details are described in connection with method step c) and FIG. 3.

Finally, the substrate 30 is tempered in method step c). Tempering is achieved by heating the substrate 30 to a specific temperature and maintaining the temperature over a specific period of time. The heating of the substrate 30 can be implemented by laser light 41 of the laser source 40 that entirely or only partially irradiates the substrate surface 31. As a result of tempering the substrate 30, the compression is again partially released, ie the surface shape deviation 32 is again changed in the opposite direction with respect to the state immediately after method step b). As mentioned in connection with method step b), this allowance of decompression can be done in advance during compression to correct the substrate surface 31 so that the intended surface shape is obtained by the last method step c) of tempering. . As an alternative, the substrate 30 can also be heated in an oven 42, as is known from a method for tempering metal. By doing so, the substrate 30 is placed in the oven 42 with all attachments for the substrate pre-assembled in place. A predetermined temperature-time curve can then be set on the oven 42, which curve leads to the desired result of the surface shape corresponding to the intended surface shape.

The reflective optical elements produced by method steps a) to c) of FIG. 2 can later be used as EUV mirrors 18, 19, 20 or as EUV reticles 7 in a projection exposure apparatus.

3A to 3C are schematic images of the substrate surface 31, generated by interferometric measurements, or the difference generated by calculation, of two images of the substrate surface 31 generated by interferometric measurements. Is shown. It should be understood that the lines a) to 3c) are contour lines, the solid line representing the rise out of the plane of the drawing and the dotted line representing the depression into the drawing plane.

Here, Fig. 3A shows the substrate surface 31 after a long irradiation period of 4000 hours with the EUV radiation used, for example. 3b) shows the substrate surface 31 of the same substrate 30 after method step b). If the difference between the two measurements is formed by calculation, it includes a homogeneous component and a heterogeneous component. The homogeneous component of the difference is much larger than the heterogeneous component, so that the heterogeneous component becomes unrelated to possible predictions of the surface shape after the method also described above. From this, a simple calculation rule is derived as follows:

Surface morphology _c) = KF × surface morphology _b) + heterogeneity difference,

here

-Surface shape _c) denotes the final surface shape of the substrate 30 obtained after method step c), i.e. tempering,

-KF represents a coefficient according to the substrate material, the geometric shape of the substrate 30 and the size of the surface correction,

-Surface shape _b) denotes the surface shape after method step b),

-Inhomogeneous differences represent poorly predictable residual errors.

As a result of the irradiation 33 it is possible to generate a model of the behavior of the material during decompression by tempering based on compression and testing, where the substrate material 30 is as described also above in method step b). As such, it was treated by irradiation 33 and thereafter by tempering according to method step c) also described above. With the help of FEM models, these models can be used to determine the coefficients (KF). Here, the FEM model may convert a stress generated through compression into a change of the substrate surface 31 in consideration of the geometric shape of the substrate 30. Here, its effect on the decompression and surface shape deviation 32 occurring in method step c) can be tolerated in advance in method step b). The method can be used to manufacture reflective optical elements 7, 18, 19, 20 with maximum long-term stability for use in EUV projection exposure apparatus. Moreover, the method can also be used to calibrate a reflective optical element whose fabrication has already been completed.

1: Projection exposure apparatus 2: Facet mirror
3: light source 4: illumination optical unit
5: Objective Field 6: Objective Plane
7: reticle 8: reticle holder
9: projection optical unit 10: image field
11: image plane 12: wafer
13: Wafer holder 14: EUV radiation
15: middle field focal plane 16: pupil facet mirror
17: assembly 18: mirror
19: mirror 20: mirror
30: substrate 31: substrate surface
32: surface shape deviation 33: irradiation
34: (compressed) substrate area 35: electron source
36: electron (radiation) 37: (virtual) area
38: protective layer 39: reflective layer
40: laser source 41: light source
42: oven

Claims (11)

A method for manufacturing a reflective optical element for a projection exposure apparatus 1 comprising a substrate 30 having a substrate surface 31, a protective layer 38 and a layer sub-system 39 suitable for the EUV wavelength range,
a) measuring the substrate surface 31,
b) irradiating the substrate 30 with the help of the electron 36,
c) tempering the substrate (30). The method of claim 1,
A method, characterized in that a temperature of 22° C. to 400° C. is used when tempering the substrate 30. The method according to claim 1 or 2,
The method, characterized in that the temperature is maintained over a period of 1 hour to 1000 hours when tempering the substrate 30. The method according to any one of claims 1 to 3,
A method, characterized in that the temperature changes over time when tempering the substrate (30). The method according to any one of claims 1 to 4,
A method, characterized in that the substrate 30 is heated in a homogeneous manner during tempering. The method according to any one of claims 1 to 4,
A method, characterized in that the substrate 30 is heated in a local manner during tempering. The method according to any one of claims 1 to 6,
The method, characterized in that the temperature is introduced into the substrate 30 by irradiation 41 with a laser 40 having a wavelength of 2.6 μm to 2.8 μm, in particular 2.755 μm. The method according to any one of claims 1 to 7,
A method, characterized in that the change of the substrate 30 as a result of tempering is taken into account during the irradiation 33 of the substrate 30 in method step b). It is a reflective optical element for the EUV wavelength range comprising a layer arrangement 39 applied to the surface of the substrate 30,
-The layer arrangement comprises at least one layer sub-system, and the substrate 30 is the average of the substrate 30 at a distance of 1 mm from the surface, in the area of the surface adjacent to the layer arrangement up to a distance of 5 μm from the surface. Has an average density greater than 0.1% by volume higher than the density,
-The substrate 30 reflects for the EUV wavelength range, having a density change of more than 0.1% by volume along the virtual region 37 at a fixed distance of at least 1 µm to 100 µm, preferably 1 µm to 30 µm from the surface. In the optical element,
A reflective optical element for the EUV wavelength range, characterized in that a temporal change in density greater than 0.1% by volume higher than the average density of the substrate 30 at a distance of 1 mm from the surface is less than 20% in the first 7 years after manufacture of the optical element. Microlithographic projection comprising a mirror (18, 19, 20) as a reflective optical element according to claim 9 and/or a mirror (18, 19, 20) as a reflective optical element manufactured according to the method of claims 1 to 8 lens. A microlithographic projection exposure apparatus (1) comprising a projection lens according to claim 10.

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